This invention relates to a high-pressure rotary fluid-displacing machine suitable for use as a motor or pump, which machine comprises a housing, an internally toothed annular gear, an externally toothed pinion arranged eccentrically within said annular gear and intermeshing therewith, an engagement-free crescent-shaped gap being left between the addendum circles of the pinion and of the annular gear, respectively, on the side thereof opposite the contact point of the pitch circle of the pinion with the pitch circle of the annular gear, a shaft bearing the pinion and being adapted for transmitting torque, and a gap-filling member in the gap having an inner and an outer curved surface, the inner surface being sealingly contacted by the addendum surfaces of the teeth of the pinion, and the outer surface being sealingly contacted by the addendum surfaces of the teeth of the annular gear.
More in particular, the invention relates to an internal gear pump or an internal gear motor with an inwardly-toothed, annular gear rotatable with constant axial clearance and radial clearance, which axially limit the working spaces between two plate members, and with an outwardly-toothed pinion mounted on a shaft for rotation therewith and meshing with the annular gear, a crescent-shaped gap-filling piece with broken-off points being provided on the side opposite to the point where the engagement of the teeth is deepest, and along which gap-filling piece the addendum surfaces of the teeth of the gears slide in a leak-proof manner.
Internal rotary machines are known which are provided with trochoidal internal gear and can operate both as pumps and as motors, and in which a sealing between low pressure and high pressure media in the region between the toothed gear rims facing each other is effected solely by the mutual cooperation of the tooth profiles of the two gears. A machine of this type is described in U.S. Pat. No. 3,619,093. In order to fulfill the well-known requirement for little leakage of the working fluid and, at the same time, high working pressures, the known machines must be built with extraordinarily tight manufacturing tolerances for the toothing which, in most cases, entails unacceptably high manufacturing costs especially in the case of internal toothing. At first sight, the construction of such machines appears to be comparatively simple, but it has been found that the volumetric delivery rate, and hence the torque increase or decrease, varies strongly with the angle of rotation so that a pulsating fluid flow or, in the case of a motor, a varying torque is the undesirable result.
In U.S. Pat. No. 3,491,698 and, particularly, 3,907,470, there are described machines with involute or trochoidal internal toothing of the type mentioned initially which, to a large extent, overcome these drawbacks by the provision of a crescent-shaped gap-filled piece, in the non-engagement region of the toothing. The main object in the conception of this machine is, however, primarily to attain a high volumetric efficiency and a high degree of counteracting or equalizing wear, and not to obtain a strict reversibility of the direction of rotation and a high starting torque on switching on the machine, wherefor these known machines fail to possess in full the last-mentioned two properties which are, however, indispensable for hydraulic motors.